Alloyed copper

ABSTRACT

Deoxidized copper having near-trace amounts of iron and possibly also chromium is alloyed with zirconium and aluminum. The resulting alloyed metal experiences a significantly delayed onset of embrittlement when stressed at elevated temperatures.

United States Patent Inventor Appl. No.

Filed Patented Assignee Herbert Greenwald, Jr. Upper Arlington, Ohio 877,879

Nov. 18, 1969 Oct. 26, l 97 1 Berry Metal Company Harmony, Pa.

ALLOYED COPPER 6 Claims, No Drawings US. Cl 1.

Int. Cl 1 lField of Search Primary ExaminerCharles N. Lovell A!torneyDaniel H. Dunbar ABSTRACT: Deoxidized copper having near-trace amounts of iron and possibly also chromium is alloyed with zirconium and aluminum. The resulting alloyed metal experiences a significantly delayed onset of embrittlement when stressed at elevated temperatures.

ALLOYED COPPER SUMMARY OF THE INVENTION Copper, such as deoxidized electrolytic copper or oxygenfree high-conductivity (OFHC) copper and having an iron content in a near-trace (approximately 50 parts per million by weight) amount, possibly a chromium content to as much as l parts per million by weight, and other elements in amounts considered to be impurities, is alloyed with zirconium in the approximate range from 0.005 percent by weight to 0.03 percent by weight in combination with aluminum in a like or even greater amount. When alloyed properly under vacuum conditions or in a metallurgically inert gaseous environment, the resulting alloyed metal develops improved resistance to embrittlement at grain boundary regions, especially under conditions of approximately 900 F. to l,000 F. and 4,000 p.s.i. tensile stress to 5,000 psi. tensile stress.

DETAILED DESCRIPTION Metallurgical examination of failed cast copper parts and failed forged copper parts, each type having been subjected to temperatures of at least 700 F. to 1,000 F. under tensile conditions estimated to involve at least 4,000 psi. to 5,000 psi. stress over prolonged periods of time, suggests that the principal phenomenon causing cracking or flaking and erosion of surface metal failures in the parts is a form of embrittlement. Such embrittlement apparently involves the preferential precipitation of iron-rich and also possibly chromium-rich material at grain boundary regions of the copper and in the form of near-continuous films either alone or with subsequent preferential oxidation or sulfidation attack on such iron and/or chromium enriched zones.

It has been discovered that the onset of such failure by embrittlement can be significantly delayed in the stressed and heated copper part, particularly at elevated temperatures where the iron-rich (and chromium-rich) materials diffuse more rapidly, by the controlled combining of zirconium and also aluminum into the copper in minimum amounts that are stoichiometrically related to the iron (and possibly chromium, if any) content of the copper. Although additions of the specified zirconium and aluminum alloying elements to the copper in amounts greater than the preferred range may not reduce the embrittlement delay that is otherwise obtained, and sometimes may even somewhat enhance the improvement, the increased amounts may have an adverse effect on other properties such as reducing electrical conductivity.

For the purpose of this invention it is preferred that the amount of zirconium added be in the range of 0.005 to 0.03 percent by weight of the total alloy. In many instances the amount of zirconium alloyed into the copper to obtain the advantages associated with this invention is in the narrower range of approximately 0.01 to 0.02 percent by weight of the total alloy.

The amount of aluminum to be alloyed into the same copper in the practice of this invention is essentially like the amount of zirconium although proportionally larger amounts of aluminum, within limits, do not appear to adversely affect the delay in onset of embrittlement that otherwise is obtained. Thus, the invention also preferably involves the addition of a corresponding amount of aluminum in the range of approximately from 0.005 to 0.03 percent by weight to the copper and often an amount in the range from 0.01 to 0.02 percent is utilized. No clear upper limit for the aluminum content is known and in at least one instance a total of 0.3 percent aluminum has been employed with a 0.02 percent zirconium addition.

It is also important in the practice of the instant invention that the alloying elements be combined with the copper in a controlled manner. In one such acceptable method of alloying the copper is vacuum melted, deoxidized by hydrogen bubbling in a partial vacuum, combined with the alloying elements under a vacuum condition, thoroughly mixed by argon bubbling in a partial vacuum, and afterwards also cast and solidified under vacuum. In an alternate acceptable method deoxidized copper is melted, alloyed, mixed, and cast and solidified entirely in a nonreactive gaseous environment such as in essentially pure argon. Exposure of the alloying elements to oxygen at metal-melting temperatures must be avoided. Also, alloying conditions should be such that the zirconium and aluminum additions not be in an oxide, nitride, or carbide form or their effectiveness will not be realized. Accordingly, it is preferred that the specified alloying ingredients be combined in their metallic form. Although not presently known, it is conjectured that homologues of the alloying elements, particularly hafnium, are operative to obtain the advantages of the instant invention.

The comparative data in the following tables I and II illustrates the significance of the instant invention with respect to effecting a delay in the onset of embrittlement under conditions of tensile stress and elevated temperatures. Table 1 provides information regarding the improved alloys; table II, on the other hand, relates to coppers alloyed in a conventional manner. In each case, however, the alloyed metal tested was prepared in a manner involving deoxidation and was subjected in tensile bar form, to a tensile stress of at least 4,000 psi. and a temperature of approximately 950 F. The time to embrittlement (rupture) under the specified test conditions is given for each of the representative melt alloy compositions indicated.

1 Tested at 5,000 p.s.i. tensile stress; subsuquvnt loading of bar to 7,000 p.s.i. tensile stress resulted in nearly iimncdiato rupture.

TABLE II Percent Condillours to tion Zirconium Aluminum Copper rupture 0 0.01 99. 97 0.2 (l 0 99.98 0.1 0. 002 0. 001 rm. 9!) 38. 3 0 0 09. 88 2. 2 0 0 00. 09 4. 0

In the foregoing tables, amounts given as zero or nil were unmeasurable and are essentially considered to be less than trace amounts (less than approximately 50 parts per million). The iron content of each alloy in each instance was determined to be less than 30 parts per million (less than 0.003 percent) by weight, such amount being derived from spectrographic analyses.

From the accomplished alloying improvements it has also been determined that the method of alloying copper with the specified amounts of zirconium and aluminum is effective to significantly reduce the iron content of the copper. In one instance it was determined that a starting copper having approximately 50 parts per million of iron by weight exhibited an iron content of 10 parts per million by weight (approximately) after the alloying with zirconium and aluminum had been completed.

lclaim:

I. An improved copper alloy consisting on a weight basis of approximately from 0.005 to 0.03 percent zirconium, at least approximately from 0.005 to 0.03 percent aluminum, and the balance except for impurities deoxidized copper.

2. The invention defined by claim I, wherein the zirconium and aluminum contents are each approximately from 0.005 to 0.01 percent.

3. The invention defined by claim I, wherein the zirconium content is approximately 0.005 percent and the aluminum content is approximately 0.01 percent.

termetallic compound.

6. The invention defined by claim 5, wherein the zirconium is combined in the copper alloy with aluminum and iron to form a stable ternary system intermetallic compound. 

1. An improved copper alloy consisting on a weight basis of approximately from 0.005 to 0.03 percent zirconium, at least approximately from 0.005 to 0.03 percent aluminum, and the balance except for impurities deoxidized copper.
 2. The invention defined by claim 1, wherein the zirconium and aluminum contents are each approximately from 0.005 to 0.01 percent.
 3. The invention defined by claim 1, wherein the zirconium content is approximately 0.005 percent and the aluminum content is approximately 0.01 percent.
 4. The invention defined by claim 1, wherein the zirconium content is approximately 0.02 percent and the aluminum Content is approximately 0.3 percent.
 5. The invention defined by claim 1, wherein the zirconium is combined in the copper alloy with iron to form a stable intermetallic compound.
 6. The invention defined by claim 5, wherein the zirconium is combined in the copper alloy with aluminum and iron to form a stable ternary system intermetallic compound. 